The 80ᚼ Pareto principle is based on Pareto's theory that 80% of the results one gets in a particular endeavour will be mainly due to 20% of areas to which one has applied efforts. In business this principle has been found to be true. Your data, properly converted into appropriate performance indicators, will show you where your largest margins come from. You can then channel more time and effort in that direction.
At times, they would prefer to click a button that says "Print ABC", or "Print XYZ" report, instead of having to crawl all over the huge spreadsheet(and get "lost" every now and then), to highlight and print different report pages. Using a custom built data entry form to make data entries into 14 different cells in different parts of a table(at the same time/with one click) would, for them, be "heaven" compared to making the entries one at a time.
I believe the foregoing are compelling justifications for choosing Excel Visual Basic over Visual Basic.
In addition, an Excel VB developer( who in many cases will tend to be a user turned developer, and is therefore likely to easily see things from your perspective) _ unlike a programmer _ is more likely to be positively disposed to working with you to ensure the application meets your practical needs. S/he will readily understand that the final application is meant to help solve a real problem(s), and will therefore build it to match those expectations.